Electron tube having concentric electrodes



Nov. 23, 1965 J. R. BEERS ELECTRON TUBE HAVING CONCENTRIC ELECTRODES Filed Oct. 7, 1960 IN VEN TOR. JOHN A. 55565 BY 3 2 g 2 United rates Patent 3,219,863 ELECTRGN TUBE HAVHNG CGNQENTRE ELECTRQDES .lohn R. Eeers, tliifton, Ni, assignor to Ling-Terrier) Electronics, lac, Newark, Ni, a corporation of Delaware Filed Get. 7, 1960, Ser. No. 61,135 6 Uairns. (Cl. 31337) This invention relates to electron tubes and more particularly to an improved electrode assembly therefor.

In the manufacture of electron tubes, particularly multigrid tubes of the power type, the problems of electrode line-up and vibrational stability are extremely important. The mass production of tubes demands that all tubes produced of a given type exhibit operating characteristics which do not materially vary from the standard or design characteristic for that type. This, of course, is important because of the necessity of replacement of tubes in actual operating circuits where reproducibility of tube characteristic is essential in obtaining the desired circuit performance. An important factor in obtaining reproducibility of tube characteristics is the maintenance of exact interelectrode spacings Within the tube, particularly in the relative spacings between the grids and cathode of multigrid tubes. If the cost of manufacture of the tubes is to be minimized, a simple and efficient electrode assembly must be employed to facilitate the use of simple assembly techniques involving a minimum of high skill labor. Additionally, it is quite important that the accuracy of interelectrode spacings be maintained when the tube is subjected to rough mechanical operating conditions, such as shock and vibration, for example, so that the electrical characteristics of the tube are not materially altered.

Accordingly, it is an object of this invention to provide an electron tube electrode assembly which simplifies the problem of electrode line-up during manufacture and which is mechanically and electrically stable under conditions of severe vibration or shock.

It is a further object of this invention to provide an electron tube electrode assembly which is rugged and dependable and which reduces the possibility of misalignment and electrical short circuit between the electrode structures of multigrid tubes.

It is a still further object of this invention to provide an electron tube electrode assembly employing a novel cathode structure which minimizes heat loss from the heated area of electron emission, to thereby permit maximum electron emissivity and tube output.

Briefly, the electron tube electrode assembly of the invention employs a central support rod of electrically conductive material to support and maintain all of the electrodes forming the assembly in predetermined spaced relationships. Spacer elements of electrical insulating material are mounted on the rod at spaced points along the length thereof adjacent the ends of the electrode structures and serve to both physically support and accurately space the electrode structures with respect to each other. The central support rod may also serve as an electrical lead for one or more of the electrode structures to further simplify the assembly. When the support rod is mounted on the header attached to the base of the tube, it is apparent that any vibration or shock to the tube during use will cause all of the electrodes mounted on the rod to be vibrated or moved together, so that the accuracy of interelectrode spacing is not disturbed. Furthermore, the use of a single central support rod with associated spaced elements mounted on the rod facilitates the accurate manufacture of the electrode assembly by means of jigs or fix tures and the like. The invention also contemplates that the cathode structure of the electrode assembly may have Patented Nov. 23, 1965 the active electron emission portion thereof separated from the inactive portion thereof by a plurality of slots arranged in staggered relationship to form a thermal barrier which prevents excessive heat loss from the heated active portion of the cathode. By preventing excessive heat loss from the active area of the cathode, electron emission and therefore tube output, is increased.

In the drawing:

FIG. 1 is a plan view of an electron tube constructed in accordance with the teachings of the invention;

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1- showing the details of construction of the electrode assembly of the tube; and

FIG. 3 is a perspective view of the cathode element of the electrode assembly illustrated in FIG. 2 showing the novel thermal barrier of the invention.

Referring now to FIGS. 1 and 2 of the drawing, there is shown a vacuum tube of the multigrid, power type having an electrode assembly constructed in accordance with the teachings of the invention. The tube comprises an envelope it) which is hermetically sealed at the lower end thereof to a circular header 11. The header 11 may be formed of glass, ceramic or other electrical insulating material, while the envelope 10 is usually formed of glass, ceramic or metal. When the envelope 10 is made of metal, the envelope itself may act as the anode electrode of the tube. However, in the design illustrated, a separate anode structure 12 is utilized. Anode 12 is cylindrical in shape and may be formed of an electrically conductive material, such as Zirconium coated graphite, for example. The anode is supported by the envelope 10 by means of an anode cap 13, a cylindrical flange element 14 and a pair of rods 15. The anode 12 is secured to the rods 15 by means of flanges 16 formed on the anode and sleeves 17 secured to the rods. The sleeves serve to prevent axial movement of the flanges 16 and hence the anode along the rods. In practice, the cylindrical flange 14 is brazed to the inside of the anode cap 13 during assembly of the tube and the rods 15 are secured by means, such as welding, for example, to the lower lip of the cylindrical flange 14. The anode cap 13 and flange 14 are usually formed of a material, such as Kovar, for example, having a thermal coeflicient of expansion very close to that of the glass envelope 10 of the tube, so that the cap 13 may be hermetically sealed to the envelope at 18 to form a vacuum or gas-tight enclosure within the envelope 1%). An exhaust tip (not shown) is usually provided at the bottom of header 11 to permit evacuation of the tube after assembly. By forming the rods 15' of an electrically conducting material, such as molybdenum, for example, the rods serve both to support the anode 12 and to provide an electrical connection between the anode and the anode cap 13 which forms the external anode terminal.

An electrode assembly, indicated generally as 19, is concentrically arranged Within the cylindrical anode structure 12 and comprises a spacer element or disc 20 formed of an electrical insulating material, such as a ceramic, for example. A central support rod 21 formed of an electrically conductive material, such as tungsten, for example, is perpendicularly mounted on the spacer element 20. As illustrated, the central support rod 21 is formed with a section 22 of reduced diameter Which passes through an aperture 23 in the support element 2.0. A sleeve 24 is welded to the section 22 of the rod at the lower surface of the spacer element 20, so that the spacer element is clamped between the shoulder formed on the rod and the sleeve 24. Obviously, other convenient methods of mounting, such as cementing, for example, may be used. Spacer element 20 is mounted on the header 1]; by means of four support conductors Z5, 26, 27 and 28 which are hermetically sealed in, and pass through, the header 11. Support conductor 23 is located behind support conductor 26 in the view taken in FIG. 2 of the drawing. Preferably, the four support conductors are formed of a conducting material, such as Kovar, for example, having a suitable thermal coeflicient of expansion for sealing to glass. The usual base of the tube having the base contact pins mounted therein is not illustrated, it being understood that the support conductors 2548 are soldered to the base pins in the usual manner in the finished assembled tube. The spacer element 20 is secured to each of the support conductors 2548 by means of sleeves 29 welded to the conductors above and below the element, so that the assembled central support rod 21 and spacer element 20 are securely connected to the header 11.

The tube illustrated has an indirectly heated cathode structure comprising cylindrical cathode element 30 and heater element 31. The bottom end of cylindrical cathode element 30 is seated in an annular groove 32 formed in spacer element 20, while the top end of the cathode is closed with a disc or cap 33 surrounding the central support rod 21. By fabricating the cap 33 of an electrically conductive material, the cathode element 30 is electrically connected to the central support rod 21, which in turn is electrically connected to support conductor 28 by means of a conducting rod 34. This arrangement permits the cathode element 30 to be connected to the base pin associated with support conductor 28. Heating element 31 may comprise a helical coil of tungsten wire which is dimensioned to fit snugly inside of the cathode 30 after it has been carefully insulated by an aluminum oxide coating which is sintered on at a predetermined thickness to keep the heater to the desired diameter. One end of the heater coil 31 is secured to the central support rod at 35 by suitable means, such as welding or soldering, for example, while the other end is electrically con nected to support conductor 25 by means of conducting rods 36 and 37, so that the heater is electrically connected between the base pins associated with support conductors 25 and 28. Although the aluminum oxide coating sintered on the heater to insulate it from the cathode may usually be made of a suificient thickness to provide the proper electrical insulation, if desired, a separate sleeve 38 of electrical insulating material may be inserted between the cathode and the heater to provide added electrical insulation.

The cathode 30 is provided with two peripherally arranged rows of slots 39 which form a thermal barrier to prevent excessive heat loss by conduction from the active electron emitting portion of the cathode above the slots. As illustrated, the slots in one row are staggered with respect to the slots of the other row, so that a slot of one row is adjacent the metal of the cathode separat ing two slots of the other row. By virtue of this arrangement, a long tortuous path is provided for conductive heat transfer between the upper active portion of the cathode and the lower inactive portion. The upper ac tive portion of the cathode is arranged to extend at least from the top to the bottom of heater coil 31 and is provided with the usual emission coating. Although for most applications, the staggered slot arrangement provides sufiicient protection against heat loss from the active cathode portion, if desired, a ceramic disc 40 may be provided below the active cathode area, as illustrated, to reduce heat loss caused by downward radiation. The disc 40 also serves the useful function of further supporting cathode element 30 with respect to the central support rod 21.

A first cylindrical grid structure 41, which may be of the squirrel-cage type, is concentrically disposed about the cathode 30 and has the lower end thereof secured to a metallic cylinder or thimble 42. The thimble 42, which may be formed of nickel, for example, is seated in an annular groove 43 formed in spacer element 20. The upper end of the grid 41 is secured by means, such as welding, for example, to a cylindrical flange 44 which is seated on an annular recessed portion or lip of a spacer disc 45 of ceramic or other insulating material. The spacer disc 45 is centrally apertured to receive central support rod 21 and is axially spaced a distance above the metallic cathode cap 33 by a cylindrical flange element 46. Grid 41 is electrically connected to one of the base pins of the tube by means of the thimble 42, a conductor rod 47 and the support conductor 27. A second cylindrical grid structure 48, which may also be of the squirrel-cage type, is concentrically disposed about the first grid structure 41 and has the lower end thereof secured, by means such as welding, to a flared thimble 4? similar to thimble 42 of the first grid. Thimble 49 is seated in an annular recessed portion or lip 50 formed in spacer element 20. The upper end of grid 48 is secured to a cylindrical flange 51 seated on a lip formed in a spacer disc 52 similar in construction to disc 45. A sleeve 53 is disposed between the spacer discs 52 and 45 on central support rod 21 to provide for adequate spacing therebetween, while a sleeve 54 is secured to the free end of the central support rod to securely clamp the entire electrode assembly. Finally, a conductor rod 55 is welded to thimble 49 and support conductor 26 to electrically connect the second grid structure 48 to one of the base connecting pins.

It is believed apparent from the foregoing description that each of the electrode structures of electrode assembly 19 is radially spaced and supported by means of the central support rod 21 and the spacer discs 26, 33, 45 and 52. The cathode 30 is supported at the lower end by annular groove 32 in spacer element 2% and at the upper end by the metallic spacer cap 33, so that it is spaced a fixed radial distance from the support rod 21. Grid 41 is supported at the lower end by annular groove 43 in spacer element 20 and at the upper end by the spaced disc 45. Similarly, grid 48 is supported at the lower end thereof by the lip 51) formed in disc 20 and at the upper end by the spacer disc 52. The heating element 31 of the cathode structure fits snuggly within the cylindrical cath ode and is secured to the central support rod 21. The annular recessed portions formed in the spacer discs provide accurate radial spacing for the electrodes and tie them to the central support rod 21. By virtue of this arrangement, when the tube is subjected to shock or severe vibration, all of the electrodes move in unison with the central support rod, thereby maintaining the accuracy of electrode alignment and preventing short circuits and variations in tube characteristics caused by misalignment. Furthermore, the use of a single, central support rod and grooved spacer discs supported by the rod facilitates accurate assembly of the parts by relatively unskilled labor. The capacitance between the cathode and each of the grids may be readily changed to meet desired values by slight changes in the thimbles 42 and 4?. It may also be noted that the central support rod 21 serves as a lead making electrical contact between the base contact pin associated with support conductor 28 and both the upper end of the heating coil 31 and the cathode 30.

It is believed apparent that many changes could be made in the above described invention and many seemingly diiferent embodiments of the invention constructed, without departing from the scope thereof. For example, although the tube illustrated is a vacuum tube of the tetr-ode type, the same construction could be used with gas tubes or tubes having a smaller or greater number of electrodes. Furthermore, although the anode structure of the illustrated tube is arranged to be separate from the main electrode assembly, it is obvious that the anode could be included as a part of the main electrode assembly with the electrical connection therefor brought out through the header 11 and connected to a base connecting pin. Additionally, the cylindrical electrodes could be replaced by electrodes of other shapes and the annular grooves in the spacer elements modified to accommodate the shapes selected. Finally, it is believed obvious that the two spacer elements 45 and 52 could be replaced by a single, properly stepped, spacer disc. Accordingly, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What i claimed is:

1. An electron tube electrode assembly comprising a central support rod of electrically conductive material; a cathode structure comprising a cylindrical cathode element surrounding said rod and a heater element disposed within said cathode element adjacent the active emitting portion of said cathode element; at least one cylindrical electrode structure concentrically disposed about said cathode element and radially spaced therefrom; a first spacer disc mounted on said rod adjacent one end of said cathode element for peripherally engaging and supporting said one end, said first spacer disc being formed of an electrically conductive material, so that said rod and disc serve as an electrical lead for said cathode element; a second spacer disc formed of an electrical insulation material mounted on said rod adjacent said first disc and one end of said electrode structure for peripherally engaging and supporting said one end of said electrode structure; and a third spacer disc formed of an electrical insulation material mounted on said rod adjacent the other end of each of said cathode and electrode structures, said third disc having at least a pair of radially spaced, concentrically arranged annular grooves formed therein for seating said other ends of said structures, so that axial and radial movements of said structures with respect to said rod are prevented.

2. An electron tube electrode assembly as claimed in claim 1, wherein one terminal of said heater element is electrically connected to said rod, so that said rod serves as an electrical lead for both said cathode element and said heater element.

3. An electron tube electrode assembly as claimed in claim 1, wherein said cathode element is provided with at least two axially spaced, peripherally arranged rows of slots separating the active and inactive portions there of, the slots of one of said rows being peripherally staggered with respect to the slots of the other of said rows, so that a long, tortuous path of heat conduction is provided between said active and inactive portions.

4. In an electron tube having an envelope and a base header sealed to said envelope, the combination comprising a central support rod of electrically conductive material; a cathode structure comprising a cylindrical cathode element and a substantially cylindrical heating element concentrically disposed within said cathode element and having one terminal thereof connected to said rod, each of said elements surrounding said rod and extending axially along the length thereof, said cathode element having an axially extending active emitting portion adjacent said heating element and an inactive portion axially extending beyond said heating element, said active and inactive cathode portions being separated by at least two axially spaced, peripherally arranged rows of slots, the slots of one row being peripherally staggered with respect to the slots of the other row, so that a long, tortuous path is provided for heat conduction between said cathode portions; a first spacer disc of electrically conductive material mounted substantially perpendicularly on said rod adjacent one end of said cathode structure for peripherally supporting and engaging said cathode element, so that said rod serves as an electrical lead for both of said cathode and heater elements; first and second concentrically arranged cylindrical grid structures concentrically disposed about said cathode structure; second and third spacer discs of electrical insulation material mounted substantially perpendicularly on said rod adjacent one end of said grid structures, each of said second and third discs having an annular recessed portion formed therein for seating the adjacent end of one of said grid structures; a fourth spacer disc of a electrical insulation material mounted substantially perpendicularly on said rod adjacent the other end of said cathode and grid structures, said fourth disc hav ing at least three radially spaced, concentrically arranged annular recessed portions formed therein for seating the adjacent ends of said cathode and grid structures; and a plurality of support conductor rods secured to said base header and said fourth spacer disc for supporting said fourth disc and serving as electrical leads for said electrode structures.

5. An electron tube electrode assembly comprising a central support rod of electrically conductive material; a plurality of electrode structures radially spaced from, and extending along said rod; means for electrically connecting at least one of said electrode structures to said rod, so that said rod serves as an electrical lead for said one structure; and a plurality of spacer elements formed of electrical insulation material mounted on said rod at spaced points along the length thereof adjacent the ends of said electrode structures, said spacer elements having recessed portions formed therein to receive the ends of said electro'de structures, so that axial and radial movements of said structures with respect to said rod are prevented, at least one of said spacer elements having a plurality of radially spaced grooves formed therein, each of said grooves having a different one of said electrode structures seated therein.

6. An electron tube electrode assembly comprising a central support rod of electrically conductive material; a plurality of radially spaced, concentrically arranged cylindrical electrode structures surrounding said rod; means for electrically connecting at least one of said electrode structures to said rod, so that said rod serves as an electrical lead for said one structure; and a plurality of spacer discs formed of an electrical insulation material mounted on said rod at spaced points along the length thereof adjacent the ends of said electrode structures, each of said discs having a surface thereof substantially perpendicular to said rod and an annular recessed portion formed in said surface for seating an end of at least one of said electrode structures, so that axial and radial movements of said structures with respect to said rod are prevented, said surface of at least one of said spacer discs being formed with a plurality of radially spaced annular grooves, each of said grooves having an end of a different one of said electrode structures seated therein, so that said one disc is adapted to support a plurality of said electrode structures.

References Cited by the Examiner UNITED STATES PATENTS 2,077,156 4/1937 Ronci 3l3260 2,197,526 4/1940 Kosack 313243 2,517,344 8/1950 Murdock 31337 2,569,847 10/1951 Eitel et al. 313--247 X 2,582,684 1/1952 Drieschman et al. 313270 X 2,639,405 5/1953 Benedict 313-27O X 2,899,589 8/1959 Reichert 313-243 2,957,997 10/1960 Manfredi 31337 DAVID J. GALVIN, Primary Examiner.

RALPH G. NILSON, JAMES D. KALLAM, Examiners. 

1. AN ELECTRON TUBE ELECTRODE ASSEMBLY COMPRISING A CENTRAL SUPPORT ROD OF ELECTRICALLY CONDUCTIVE MATERIAL; A CATHODE STRUCTURE COMPRISING A CYLINDRICAL CATHODE ELEMENT SURROUNDING SAID ROD AND A HEATER ELEMENT DISPOSED WITHIN SAID CATHODE ELEMENT ADJACENT THE ACTIVE EMITTING PORTION OF SAID CATHODE ELEMENT ADJACENT THE ACTIVE EMITTING ELECTRODE STRUCTURE CONCENTRICALLY DISPOSED ABOUT SAID CATHODE ELEMENT AND RADIALLY SPACED THEREFROM; A FIRST SPACER DISC MOUNTED FOR PERIPHERALLY ENGAGING AND SUPPORTING CATHODE ELEMENT FOR PERIPHERALLY ENGAGING AND SUPPORTING SAID ONE END, SAID FIRST SPACED DISC BEING FORMED OF AN ELECTRICALLY CONDUCTIVE MATERIAL, SO THAT SAID ROD AND DISC SERVE AS AN ELECTRICAL LEAD FOR SAID CATHODE ELEMENT; A SECOND SPACER DISC FORMED OF AN ELECTRICAL INSULATION MATERIAL MOUNTED ON SAID ROD ADJACENT SAID FIRST DISC AND ONE END OF SAID ELECTRODE STRUCTURE FOR PERIPHEALLY ENGAGING AND SUPPORTING SAID ONE END OF SAID ELECTRODE STRUCTURE; AND A THIRD SPACER DISC FORMED OF AN ELECTRICAL INSULATION MATERIAL MOUNTED ON SAID ROD ADJACENT THE OTHER 